Spectacle-glass.



M. VON ROHR.

SPEGTAGLB GLASS.

APPLICATION FILED AUG. 25, 1910.

Patented June 18, 1912.

. mounting the I ED STATES PATENT:

MOBITZ VON BOHR, OE JENA,

emmanx, ASSIGNOR TO-THE FIRM OF CARL ZEISS, 0F JENA, GERMANY.

. srEcrAcLn-emss;

Specification of Letters Patent.

Application filed August 25, 1910. Serial No. 578,861.

Patented June 18, i912.

To all whom it may concern Be it known that I, MORITZ VON Rona, acitizen of the German Empire, residing at Carl-Zeiss strasse, Jena, inthe Grand Duchy of Saxe-Weimar, Germany, have invented a new and usefulSpectacle-Glass, of which the following is a specification.

The invention relates to spectacle glasses, collective as well asdispers1ve ones, which are cut out eccentrically for the purpose ofobtaining a prismatic efl'ect, which correctsthe eye for strabismus.This efiect occurs, as is well-known, in the plane whlch 1s given on theone hand by the optlcal axis of the glass, and on the other hand bythecenter of the latter, which is eccentric to this axis (and throughwhich the rincipal line of vision passes). The spectac e glasses of thistype, used hitherto, have according to the amount of their power more orless astigmatism, even along the principal line of vision. This wouldstill be the case with the slightly curved glasses difter Ostwalt, whichin their ordinary use, i. e., when out out concentrically, areanastigmatic even for oblique lines of vision.

tacle glasses is caused by the necessity of so glass before the eye,that all diameters of its marginand so also the one that lies in theplane of the prismatic eil'ectintersect the principal line of vision,which passes through the center of the glass,

' approximately at right angles. It is the consequence of thisunavoidable condition,

- that the optical axis of the eccentrlcally cut out spectacle glasscomes to lie more or less parallel to the principal line-of vision.

But the glasses after Ostwalt have their anastigmatic property onlyunder the assumption that the point-of intersection of the lines ofvision, the point of rotation of the eye, which has a distance of about3 cm.

- from the center of the glass, lies in the optical axis. According tothe present invention an anastigmatic spectacle glass of a certain kind,which is cut out eccentrically and placed, with a distance of about 3.cm. between its center and the said point of rotation, in the positionrelative to the principal line of vision as above specified, fulfils'thecondition that the optical axis passes through the point of rotation ofthe eye, so

that the anastigmatic effect of the glass is The above-memtioned defectof eccentrically cut out specmatically corrected spectacle glass of theWollaston form, because oji itsstrong mean curvature, the center ofwhich coincides approximately with the point of rotation of the eye,retains its anastigmatic property when out out eccentrically.

In the annexed. drawing: Figure 1 isa horizontal section through aspectacle glass of the .Wollaston form, constructed according to theinvention. Fig. 2 is a horizontal sectlen through another form of such aY glass. Both glasses are corrected astigmatically. They are cut outeccentrically in such a manner as to cause the plane of the prismaticefiect to lie horizontally.

The glass shown in Fig. 1 is intended for the correction of a myopiceye. The power in the direction of the optlcal axis is assumed to be 5dptr. The refractive index a of the kind of glass used is 1.52. The

thickness (Z of the glass in the optical axis is 0.5 mm. The section Zof this axis between the glass and the point 0, where the lines ofvision have to intersect each other, measures 25 mm. Of the two radii ofcurvature the outer one 1", is 27.5 mm., the inner one r, 21.7 mm. lon Adeflection u, of the principal line 0 vision (which passes through thecenter of the glass and inter- .sects the optical axis in O) of 3.4 or 6ctrd. (centrad) was to be obtained. For

this purpose the optical axis had to receive an inclination v of 30.7relatively to the principal line of vision. Another line of vision,inclined by 2 o relatively to the optical axis, would then experience adefiection a, of 58. The horizontal diameter of the edge, by which theglass is intended to be mounted, is shown as a dotted line a b. Itintersects the principal line of vision at right angles.

The spectacle glass according to 2 is collective and is intended toserve forthe correction of a hypermetropic eye. The power in the axis 1sassumed to be 4 (1 tr. The refractive index 72 is again 1.52. he

thickness'd is 6.0, the distance Z again 25- mm. The outer radius r hasa len h of v 29.4, the inner one 7 of 34.7 mm. T e de- An astigmaticallycorrected spectacle glass, having a convex front surface and a concavehinder surface and cut out eccerr- 15 trically forobtaining prismaticefiect, the power of the convex surface amount to a not less than 16 andnot more than 21 tr.

MORITZ volv ROHIE. Witnesses:

PAULKRfiann, Amman MECKEDANZ.

